Organic electroluminescent materials and devices

ABSTRACT

Novel heteroleptic iridium complexes having the structure of Formula I, 
                         
are provided. In Formula I, X is selected from the group consisting of NR, BR, and Se; R is selected from hydrogen and alkyl, and each R 1 , R 2 , R 3 , and R 4  is independently selected from hydrogen, alkyl, and aryl. The compounds may be used in organic light emitting devices, particularly as emitting dopants, to provide devices having improved efficiency, lifetime, and manufacturing.

This application is a continuation of U.S. application Ser. No.12/727,615, filed Mar. 19, 2010, which claims priority to U.S.Provisional Application No. 61/162,476, filed Mar. 23, 2009, thedisclosures of which are herein expressly incorporated by reference intheir entirety.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to novel organic complexes that may beadvantageously used in organic light emitting devices. Moreparticularly, the present invention relates to novel heterolepticiridium complexes containing a pyridyl dibenzo-substituted ligand anddevices containing these compounds.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

Novel phosphorescent emissive compounds are provided. The compoundscomprise heteroleptic iridium complexes having the formula:

The compound comprises a ligand having the structure

X is selected from the group consisting of NR, O, S, BR, and Se. R isselected from hydrogen and alkyl. Preferably, R has 4 or fewer carbonatoms. R₁, R₂, R₃, and R₄ may represent mono, di, tri, or tetrasubstitutions. Each of R₁, R₂, R₃, and R₄ are independently selectedfrom the group consisting of hydrogen, alkyl, and aryl. Preferably,alkyls in the R₁, R₂, R₃ and/or R₄ positions of Formula I have four orfewer carbon atoms (e.g., methyl, ethyl, propyl, butyl, and isobutyl).Preferably, R₁ and R₄ are independently hydrogen or alkyl having four orfewer carbon atoms; more preferably, R₁ and R₄ are independentlyhydrogen or methyl. Preferably, R₂ and R₃ are independently hydrogen oralkyl having four or fewer carbon atoms; more preferably, R₂ and R₃ areindependently hydrogen or methyl; most preferably, R₂ and R₃ arehydrogen.

Preferably, R₁ and R₄ are independently hydrogen, alkyl having four orfewer carbon atoms or aryl with 6 or fewer atoms in the ring; morepreferably, R₁ and R₄ are independently hydrogen, methyl or phenyl.Preferably, R₂ and R₃ are independently hydrogen, alkyl having four orfewer carbon atoms or aryl with 6 or fewer atoms in the ring; morepreferably, R₂ and R₃ are independently hydrogen, methyl or phenyl; mostpreferably, R₂ and R₃ are hydrogen.

In one aspect, compounds are provided wherein R₁, R₂, R₃, and R₄ areindependently selected from the group consisting of hydrogen and alkylhaving four or fewer carbon atoms. In another aspect, compounds areprovided wherein R₁, R₂, R₃, and R₄ are independently selected from thegroup consisting of hydrogen and methyl. In yet another aspect,compounds are provided wherein R₁, R₂, R₃, and R₄ are hydrogen.

In another aspect, compounds are provided wherein R₁, R₂, R₃, and R₄ areindependently selected from the group consisting of hydrogen, alkylhaving four or fewer carbon atoms and aryl with 6 or fewer atoms in thering. In another aspect, compounds are provided wherein R₁, R₂, R₃, andR₄ are independently selected from the group consisting of hydrogen,methyl and phenyl. In yet another aspect, compounds are provided whereinR₁, R₂, R₃, and R₄ are hydrogen.

Particular heteroleptic iridium complexes are also provided. In oneaspect, heteroleptic iridium complexes are provided having the formula:

In another aspect, heteroleptic iridium complexes are provided havingthe formula:

In yet another aspect, heteroleptic iridium complexes are providedhaving the formula:

Specific examples of heteroleptic iridium complex are provided includingCompounds 1-36. In particular, heteroleptic compounds are providedwherein X is O (i.e., pyridyl dibenzofuran), for example, Compounds1-12. Additionally, heteroleptic compounds are provided wherein X is S(i.e., pyridyl dibenzothiophene), for example, Compounds 13-24.Moreover, heteroleptic compounds are provided wherein X is NR (i.e.,pyridyl carbazole), for example, Compounds 25-36.

Additional specific examples of heteroleptic iridium complexes areprovided, including Compounds 37-108. In particular, heterolepticcompounds are provided wherein X is O, for example, Compounds 37-60.Further, heteroleptic compounds are provided wherein X is S, forexample, Compounds 61-84. Moreover, heteroleptic compounds are providedwherein X is NR, for example, Compounds 85-108.

Additionally, an organic light emitting device is also provided. Thedevice has an anode, a cathode, and an organic layer disposed betweenthe anode and the cathode, where the organic layer comprises a compoundhaving FORMULA I. In particular, the organic layer of the device maycomprise a compound selected from Compounds 1-36. The organic layer mayfurther comprise a host. Preferably, the host contains a triphenylenemoiety and a dibenzothiophene moiety. More preferably, the host has theformula:

R′₁, R′₂, R′₃, R′₄, R′₅, and R′₆ may represent mono, di, tri, or tetrasubstitutions. R′₁, R′₂, R′₃, R′₄, R′₅, and R′₆ are independentlyselected from the group consisting of hydrogen, alkyl, and aryl.

The organic layer of the device may comprise a compound selected fromthe group consisting of Compounds 1-108. In particular, the organiclayer of the device may also comprise a compound selected from Compounds37-108.

A consumer product comprising a device is also provided. The devicecontains an anode, a cathode, and an organic layer disposed between theanode and the cathode, where the organic layer further comprises acompound having FORMULA I.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows a heteroleptic iridium complex.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. Pat. No. 7,431,968, which is incorporated by reference in itsentirety. Other suitable deposition methods include spin coating andother solution based processes. Solution based processes are preferablycarried out in nitrogen Or an inert atmosphere. For the other layers,preferred methods include thermal evaporation. Preferred patterningmethods include deposition through a mask, cold welding such asdescribed in U.S. Pat. Nos. 6,294,398 and 6,468,819, which areincorporated by reference in their entireties, and patterning associatedwith some of the deposition methods such as inkjet and OVJD. Othermethods may also be used, The materials to be deposited may be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing,Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

Novel compounds are provided, the compounds comprising a heterolepticiridium complex (illustrated in FIG. 3). In particular, the complex hastwo phenylpyridine ligands and one ligand having the structure

The ligand having the structure FORMULA II consists of a pyridine joinedto a dibenzofuran, dibenzothiophene, carbazole, dibenzoborole, ordibenzoselenophene (herein also referred to as “pyridyldibenzo-substituted”). These compounds may be advantageously used inorganic light emitting devices as an emitting dopant in an emissivelayer.

Iridium complexes containing two or three pyridyl dibenzofuran,dibenzothiophene, carbazole, and fluorene ligands have been reported. Byreplacing the phenyl group in tris(2-phenylpyridine)iridium withdibenzofuran, dibenzothiophene, carbazole, and fluorene groups, theHOMO-LUMO energy levels, photophysical properties, and electronicproperties of the resulting complex can be significantly affected. Avariety of emission colors, ranging from green to red, have beenachieved by using complexes with different combinations of pyridyldibenzo-substituted ligands (i.e., bis and tris complexes). However, theexisting complexes may have practical limitations. For example, iridiumcomplexes having two or three of these types of ligands (e.g., pyridyldibenzofuran, dibenzothiophene, or carbazole) have high molecularweights, which often results in a high sublimation temperature. In someinstances, these complexes can become non-sublimable due to theincreased molecular weight. For example,tris(2-(dibenzo[b,d]furan-4-yl)pyridine)Iridium(III) decomposed duringsublimation attempts. Additionally, known compounds comprising a pyridylfluorene ligand may have reduced stability. Fluorene groups (e.g., C═Oand CRR′) disrupt conjugation within the ligand structure resulting in adiminished ability to stabilize electrons. Therefore, compounds with thebeneficial properties of pyridyl dibenzo-substituted ligands (e.g.,dibenzofuran, dibenzothiophene, carbazole, dibenzoborole, anddibenzoselenophene) and a relatively low sublimation temperature aredesirable.

Additionally, iridium complexes having two or three of the ligandshaving FORMULA II have high molecular weights and strongerintermolecular interactions, which often results in a high sublimationtemperature. In some instances, these complexes can becomenon-sublimable due to the increased molecular weight and strongintermolecular interactions.

Novel heteroleptic iridium complexes are provided herein. The complexescontain pyridyl dibenzo-substituted ligands having the structure FORMULAII. In particular, the novel heteroleptic complexes include a singlepyridyl dibenzo-substituted ligand wherein the ligand contains O, S, N,Se, or B (i.e. the ligand is pyridyl dibenzofuran, pyridyldibenzothiophene, pyridyl carbazole, pyridyl dibenzoselenophene, orpyridyl dibenzoborole) and two phenylpyridine ligands. As a result ofthe particular combination of ligands in the heteroleptic compoundsdisclosed herein, these compounds can provide both improvedphotochemical and electrical properties as well as improved devicemanufacturing. In particular, by containing only one of thedibenzo-substituted pyridine ligands having FORMULA II, the complexesprovided herein will likely have lower sublimation temperatures(correlated with reduced molecular weight and/or weaker intermolecularinteractions). Additionally, these compounds maintain all of thebenefits associated with the pyridyl dibenzo-substituted ligand, such asimproved stability, efficiency, and narrow line width. Therefore, thesecompounds may be used to provide improved organic light emitting devicesand improved commercial products comprising such devices. In particular,these compounds may be particularly useful in red and greenphosphorescent organic light emitting devices (PHOLEDs).

As mentioned previously, bis or tris iridium complexes containingligands having FORMULA II may be limited in practical use due to thehigh sublimation temperature of the complex. The invention compounds,however, have a lower sublimation temperature which can improve devicemanufacturing. Table 1 provides the sublimation temperature for severalcompounds provided herein and the corresponding bis or tris complex. Forexample, Compound 1 has a sublimation temperature of 243° C. while thecorresponding tris complex fails to sublime. Additionally, other triscomplexes comprising three pyridyl dibenzo-substituted ligands (i.e.,tris complex comprising pyridyl dibenzothiophene) fail to sublime.Therefore, the compounds provided herein may allow for improved devicemanufacturing as compared to previously reported bis and tris compounds.

TABLE 1 Sublimation temperature Compounds (° C.)

  Compound 1 243

Fail to sublime

Fail to sublime

  Compound 4 218

  Compound 29 230

290

  Compound 2 232

  Compound 7 256

  Compound 10 240

  Compound 37 224

Generally, the dibenzo-substituted pyridine ligand would be expected tohave lower triplet energy than the phenylpyridine ligand, andconsequently the dibenzo-substituted pyridine ligand would be expectedto control the emission properties of the compound. Therefore,modifications to the dibenzo-substituted pyridine ligand may be used totune the emission properties of the compound. The compounds disclosedherein contain a dibenzo-substituted pyridine ligand containing aheteroatom (e.g., O, S, or NR) and optionally further substituted bychemical groups at the R₁ and R₄ positions. Thus, the emissionproperties of the compounds may be tuned by selection of a particularheteroatom and/or varying the substituents present on thedibenzo-substituted pyridine ligand.

The compounds described herein comprise heteroleptic iridium complexeshaving the formula:

Features of the compounds having FORMULA I include comprising one ligandhaving the structure

and two phenylpyridine ligands that may have further substitution,wherein all ligands are coordinated to Ir.

X is selected from the group consisting of NR, O, S, BR, and Se. R isselected from hydrogen and alkyl. R₁, R₂, R₃ and R₄ may represent mono,di, tri, or tetra substitutions; and each of R₁, R₂, R₃ and R₄ areindependently selected from the group consisting of hydrogen, alkylhaving four or fewer carbon atoms, and aryl.

In another aspect, R₁, R₂, R₃ and R₄ are independently selected from thegroup consisting of hydrogen, alkyl having four or fewer carbon atoms,and aryl with 6 or fewer atoms in the ring.

The term “aryl” as used herein refers to an aryl, comprising eithercarbon atoms or heteroatoms, that is not fused to the phenyl ring of thephenylpyridine ligand (i.e., aryl is a non-fused aryl). The term “aryl”as used herein contemplates single-ring groups and polycyclic ringsystems. The polycyclic rings may have two or more rings in which twocarbons are common by two adjoining rings (the rings are “fused”)wherein at least one of the rings is aromatic, e.g., the other rings canbe cycloalkyls, cycloalkenyls, aryl, heterocycles and/or heteroaryls.Additionally, the aryl group may be optionally substituted with one ormore substituents selected from halo, CN, CO₂R, C(O)R, NR₂,cyclic-amino, NO₂, and OR. “Aryl” also encompasses a heteroaryl, such assingle-ring hetero-aromatic groups that may include from one to threeheteroatoms, for example, pyrrole, furan, thiophene, imidazole, oxazole,thiazole, triazole, pyrazole, pyridine, pyrazine and pyrimidine, and thelike. This includes polycyclic hetero-aromatic systems having two ormore rings in which two atoms are common to two adjoining rings (therings are “fused”) wherein at least one of the rings is a heteroaryl,e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl,heterocycles and/or heteroaryls. Additionally, the heteroaryl group maybe optionally substituted with one or more substituents selected fromhalo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR. For example, R₁,R₂, R₃ and/or R₄ may be an aryl, including an heteroaryl, that is notused to the phenyl ring of the phenylpyridine.

The term “alkyl” as used herein contemplates both straight and branchedchain alkyl radicals. Examples include methyl, ethyl, propyl, isopropyl,butyl, isobutyl, tert-butyl, and the like. Additionally, the alkyl groupmay be optionally substituted with one or more substituents selectedfrom halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR, wherein eachR is independently selected from H, alkyl, alkenyl, alkynyl, aralkyl,aryl and heteroaryl. Preferably, in order to make the compoundssublimable and/or to reduce sublimation temperature, alkyls in the R₁,R₂, R₃ and/or R₄ positions of Formula I have four or fewer carbon atoms(e.g., methyl, ethyl, propyl, butyl, and isobutyl).

In general, the compounds provided herein have relatively lowsublimation temperatures compared to previously reported compounds.Thus, these novel compounds provide improved device fabrication amongother beneficial properties. Moreover, it is believed that heterolepticcompounds having FORMULA I wherein R₁, R₂, R₃ and R₄ are selected fromsmaller substituents may be particularly beneficial. A smallersubstituents includes, for example, hydrogen or alkyl. In particular, itis believed that compounds wherein the substituents R₁, R₂, R₃ and/or R₄are selected from smaller substituents may have even lower sublimationtemperatures thereby further improving manufacturing while maintainingthe desirable properties (e.g., improved stability and lifetimes)provided by the ligand having the structure FORMULA II.

Generally, the compounds provided having FORMULA I have substituentssuch that R₁, R₂, R₃ and R₄ are independently selected from the groupconsisting of hydrogen, alkyl, and aryl. Preferably, any alkyl has fouror fewer carbon atoms. To minimize molecular weight and thereby lowerthe sublimation temperature, compounds having smaller substituents onthe ligand having the structure FORMULA II are preferred. Preferably, R₁and R₄ are independently selected from the group consisting of hydrogenand alkyl having four or fewer carbon atoms; more preferably, R₁ and R₄are independently selected from the group consisting of hydrogen andmethyl.

For similar reasons, compounds are preferred having smaller substituentspresent on the phenylpyridine ligand. Additionally, the phenylpyridineligand is believed to contribute less to the emission of the complex.Moreover, the complex contains two of the phenylpyridine ligand, thussubstituents present on the phenylpyridine ligand contribute more to theoverall molecular weight of the complex. For at least these reasons,preferably R₂ and R₃ are independently selected from hydrogen and alkylhaving four or fewer carbon atoms; more preferably, R₂ and R₃ areindependently selected from hydrogen and methyl; most preferably, R₂ andR₃ are hydrogen.

Compounds having alkyl and aryl substitutions that can decreaseintermolecular interactions are also preferred.

In another aspect, preferably R₂ and R₃ are independently selected fromhydrogen, alkyl having four or fewer carbon atoms and aryl with 6 orfewer atoms in the ring; more preferably, R₂ and R₃ are independentlyselected from hydrogen, methyl and phenyl; most preferably, R₂ and R₃are hydrogen.

Compounds are preferred wherein the overall molecular weight of thecomplex is low to reduce the sublimation temperature and improve devicemanufacturing. Toward this end, compounds wherein all substituents arerelatively small are preferred. In one aspect, preferably R₁, R₂, R₃ andR₄ are independently selected from the group consisting of hydrogen andalkyl having four or fewer carbon atoms; more preferably, R₁, R₂, R₃ andR₄ are independently selected from the group consisting of hydrogen andmethyl; most preferably, R₁, R₂, R₃ and R₄ are hydrogen.

In another aspect, preferably R₁, R₂, R₃ and R₄ are independentlyselected from the group consisting of hydrogen, alkyl having four orfewer carbon atoms and aryl with 6 or fewer atoms in the ring; morepreferably, R₁, R₂, R₃ and R₄ are independently selected from the groupconsisting of hydrogen, methyl and phenyl; most preferably, R₁, R₂, R₃and R₄ are hydrogen.

As discussed above, X can also be BR. Preferably, R has 4 or fewercarbon atoms. For similar reasons as those previously discussed, smalleralkyl groups (i.e., alkyls having 4 or fewer carbon atoms) on thecarbazole portion of the substituted ligand will likely lower thesublimation temperature of the complex and thus improve devicemanufacturing.

Particular heteroleptic iridium complexes are also provided. In oneaspect, heteroleptic iridium complexes are provided having the formula:

In another aspect, heteroleptic iridium complexes are provided havingthe formula:

In yet another aspect, heteroleptic iridium complexes are providedhaving the formula:

Specific examples of heteroleptic iridium complexes are provided, andinclude compounds selected from the group consisting of:

Additional specific examples of heteroleptic iridium complexes areprovided, and include compounds selected from the group consisting of:

The heteroleptic iridium compound may be selected from the groupconsisting of Compound 1-Compound 108.

Compounds having FORMULA I in which X is selected from O, S and NR maybe particularly advantageous. Without being bound by theory, it isthought that the aromaticity of the ligands comprising a dibenzofuran,dibenzothiophene or carbazole moiety (i.e., X is O, S, or NR) provideselectron delocalization which may result in improved compound stabilityand improved devices. Moreover, it is believed that compounds wherein Xis O may be more preferable than compounds wherein X is S or NR. In manycases, dibenzofuran containing compounds and devices comprising suchcompounds demonstrate especially desirable properties.

In one aspect, compounds are provided wherein X is O. Exemplarycompounds where X is O include, but are not limited to, Compounds 1-12.Compounds wherein X is O may be especially preferred at least becausethese compounds may generate devices having desirable properties. Forexample, these compounds may provide devices having improved efficiencyand a long lifetime. Additionally, the reduced sublimation temperatureof these compounds can also result in improved manufacturing of suchdesirable devices.

Additional exemplary compounds where X is O are provided and include,without limitation, Compounds 37-60. Compounds 1-12 and 37-60 mayprovide devices having improved efficiency, lifetime, and manufacturing.

In another aspect, compounds are provided wherein X is S. Exemplarycompounds where X is S include, but are not limited to, Compounds 13-24.These compounds, containing a pyridyl dibenzofuran ligand, may also beused in devices demonstrating good properties. For example, compoundswherein X is S may provide devices having improved stability andmanufacturing.

Additional exemplary compounds where X is S are provided and include,without limitation, Compounds 61-84. Compounds 13-24 and 61-84 mayprovide devices having improved stability and manufacturing.

In yet another aspect, compounds are provided wherein X is NR. Exemplarycompounds wherein X is NR include, but are not limited to, Compounds25-36. These compounds containing a pyridyl carbazole ligand may also beused to provide devices having good properties, such as improvedefficiency.

Additional exemplary compounds where X is NR are provided and include,without limitation, Compounds 85-108. Compounds 26-36 and 85-108 mayprovide devices having improved efficiency.

Additionally, an organic light emitting device is also provided. Thedevice comprises an anode, a cathode, and an organic layer disposedbetween the anode and the cathode, wherein the organic layer comprises acompound having FORMULA I. X is selected from the group consisting ofNR, O, S, BR, and Se. R is selected from hydrogen and alkyl. Preferably,R has 4 or fewer carbon atoms. R₁, R₂, R₃ and R₄ may represent mono, di,tri, or tetra substitutions. Each of R₁, R₂, R₃ and R₄ are independentlyselected from the group consisting of hydrogen, alkyl having four orfewer carbon atoms, and aryl. Preferably, R₂ and R₃ are independentlyselected from the group consisting of hydrogen and alkyl having four orfewer carbon atoms. Selections for the heteroatoms and substituentsdescribed as preferred for the compound of FORMULA I are also preferredfor use in a device that includes a compound having FORMULA I. Theseselections include those described for X, R, R₁, R₂ and R₃ and R₄.

In another aspect, each of R₁, R₂, R₃ and R₄ are independently selectedfrom the group consisting of hydrogen, alkyl having four or fewer carbonatoms, and aryl with 6 or fewer atoms in the ring. Preferably, R₂ and R₃are independently selected from the group consisting of hydrogen, alkylhaving four or fewer carbon atoms and aryl with 6 or fewer atoms in thering.

In particular, devices are provided wherein the compound is selectedfrom the group consisting of Compounds 1-36.

In addition, devices are provided which contain a compound selected fromthe group consisting of Compounds 37-108. Moreover, the devices providedmay contain a compound selected from the group consisting of Compounds1-108.

In one aspect, the organic layer is an emissive layer and the compoundhaving FORMULA I is an emitting dopant. The organic layer may furthercomprise a host. Preferably, the host comprises a triphenylene moietyand a dibenzothiophene moiety. More preferably, the host has theformula:

R′₁, R′₂, R′₃, R′₄, R′₅, and R′₆ may represent mono, di, tri, or tetrasubstitutions. Each of R′₁, R′₂, R′₃, R′₄, R′₅, and R′₆ areindependently selected from the group consisting of hydrogen, alkyl, andaryl.

As discussed above, the heteroleptic compounds provided herein may beadvantageously used in organic light emitting devices to provide deviceshaving desirable properties such as improved lifetime, stability andmanufacturing.

A consumer product comprising a device is also provided. The devicefurther comprises an anode, a cathode, and an organic layer. The organiclayer further comprises a heteroleptic iridium complex having FORMULA I.

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 2below. Table 2 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

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EXPERIMENTAL Compound Examples Example 1. Synthesis of Compound 1

Synthesis of 2-(dibenzo[b,d]furan-4-yl)pyridine

4-dibenzofuranboronic acid (5.0 g, 23.6 mmol), 2-chloropyridine (2.2 g,20 mmol), dicyclohexyl(2′,6′-dimethoxybiphenyl-2-yl)phosphine (S-Phos)(0.36 g, 0.8 mmol), and potassium phosphate (11.4 g, 50 mmol) were mixedin 100 mL of toluene and 10 mL of water. Nitrogen is bubbled directlyinto the mixture for 30 minutes. Next, Pd₂(dba)₃ was added (0.18 g, 0.2mmol) and the mixture was heated to reflux under nitrogen for 8 h. Themixture was cooled and the organic layer was separated. The organiclayers are washed with brine, dried over magnesium sulfate, filtered,and evaporated to a residue. The residue was purified by columnchromatography eluting with dichloromethane. 4.5 g of desired productwas obtained after purification.

Synthesis of Compound 1

The iridium triflate precursor (0.97 g, 1.4 mmol) and2-(dibenzo[b,d]furan-4-yl)pyridine (1.0 g, 4.08 mmol) were mixed in 50mL of ethanol. The mixture was heated at reflux for 24 h under nitrogen.Precipitate formed during reflux. The reaction mixture was filteredthrough a celite bed. The product was washed with methanol and hexanes.The solid was dissolved in dichloromethane and purified by column using1:1 of dichloromethane and hexanes. 0.9 g of pure product was obtainedafter the column purification. (HPLC purity: 99.9%)

Example 2. Synthesis of Compound 2

Synthesis of 3-nitrodibenzofuran

To 80 mL trifluroacetic acid in a 250 mL round bottom flask was addeddibenzofuran (7.06 g, 42 mmol) and stirred vigorously to dissolve thecontent at room temperature. The solution was then cooled on ice and 1.2equivalent 70% HNO₃ (4.54 g, 50.40 mmol) in 20 mL trifluroacetic acidwas poured into the stirred solution slowly. After stirring for 30minutes contents from the flask was poured into 150 mL ice-water andstirred for another 15 minutes. Off white color precipitate was thenfiltered out and finally washed with 2M NaOH and water. Moist materialwas then recrystallized from 1.5 L boiling ethanol in the form of lightyellow color crystal. 7.2 g of product was isolated.

Synthesis of 3-aminodibenzofuran

3-nitrodibenzofuran (6.2 g, 29.08 mmol) was dissolved in 360 mL ethylacetate and was degassed 5 minutes by passing nitrogen gas through thesolution. 500 mg of Pd/C was added to the solution and the content washydrogenated at 60 psi pressure. Reaction was let go until pressure inhydrogenation apparatus stabilizes at 60 psi for 15 minutes. Reactioncontent was then filtered through a small celite pad and off white colorproduct was obtained. (5.3 g, 28.9 mmol)

Synthesis of 3-bromodibenzofuran

NaNO₂ (2.21 g, 32.05 mmol) was dissolved in 20 mL conc. H₂SO₄ in conicalflask kept at 0° C. Solution of 2-aminodibenzofuran (5.3 g, 28.9 mmol)in minimum volume of glacial acetic acid was then slowly added to theflask so that temperature never raised above 5-8° C. and the mixture wasstirred at 0° C. for another 1.5 h. 100 mL ether was added to thestirred mixture and precipitate of corresponding diazo salt immediatelysettled down. Brown color diazo salt was immediately filtered out andtransferred to a flask containing CuBr (6.25 g, 43.5 mmol) in 150 mL 48%HBr. The flask was then placed in a water bath maintained at 64° C. andstirred for 2 h. After cooling down to room temperature, the dark colorreaction content was filtered out and the precipitate was washed withwater twice. Isolated solid was then flashed over Silica gel column with5-10% DCM/Hexane to give 4.79 g final compound.

Synthesis of2-(dibenzo[b,d]furan-3-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

3-bromodibenzofuran (4.79 g, 19.39 mmol), bispinacolatodiboron (6.4 g,25.2 mmol), KOAc (7.61 g, 77.54 mmol) was added to 100 mL of dioxane ina r.b. flask. Content was degassed for 30 minutes under bubblingnitrogen gas and Pd(dppf)₂Cl₂ (158 mg, 0.019 mmol) was added to thereaction mixture. After degassing for another 10 minutes, the reactionmixture was heated to 80° C. and stirred overnight. Reaction flask wasthen cooled to room temperature and filtered through a pad of celite.Deep brown color solution was then partitioned in between brine andethyl acetate. Organic layer was collected, dried over anhydrous Na₂SO₄and excess solvent was evaporated under vacuum. Brown colored solid wasthen dry loaded in silica gel column and quickly flashed with 5%ethylacetate/hexane/0.005% triethylamine to give 5.08 g final product.

Synthesis of 2-(dibenzofuran-3-yl)pyridine

Dibenzofuran boronate ester (5.85 g, 20 mmol), 2-bromopyridine (2.93 mL,30 mmol), 30 mL 2 M Na₂CO₃ (60 mmol) was slurried in 200 mLtoluene/ethanol (1:1) in a 500 mL 3-neck round bottom flask and degassedfor 30 minutes under bubbling nitrogen gas. Pd(dppf)₂Cl₂ (160 mg, 0.2mmol) was added to the slurry and degassing continued for another 10minutes. The reaction contents were then refluxed overnight. Reactioncontent was cooled to room temperature and filtered thru a small celitepad. Brown color biphasic solution was then partitioned between brineand ethylacetate. Organic layer was dried over anhydrous Na₂SO₄ andexcess solvent was removed under vacuum. Residue from previous step wasdry loaded in silica gel column and eluted with 5-8% ethylacetate/hexaneto give 4.3 g final product.

Synthesis of Compound 2

The iridium triflate precursor (2.8 g, 3.9 mmol),2-(dibenzofuran-3-yl)pyridine (4 g, 16.3 mmol) were refluxed in 100 mLethanol overnight. Bright yellow precipitate was filtered out, dried anddry loaded in a silica gel column. 210 mg final compound was isolatedafter elution with 3:2 DCM/hexane.

Example 3. Synthesis of Compound 4

Synthesis of Compound 4

The iridium triflate precursor (1.6 g, 2.2 mmol) and2-(dibenzo[b,d]furan-4-yl)pyridine (1.6 g, 6.5 mmol) were mixed in 50 mLof ethanol. The mixture was heated at reflux for 24 h under nitrogen.Precipitate formed during reflux. The reaction mixture was filteredthrough a celite bed. The product was washed with methanol and hexanes.The solid was dissolved in dichloromethane and purified by column using1:1 of dichloromethane and hexanes. 1.4 g of pure product was obtainedafter the column purification.

Example 4. Synthesis of Compound 10

Synthesis of 4-methyl-2-(dibenzo[b,d]furan-4-yl)pyridine

4-dibenzofuranboronic acid (5.0 g, 23.6 mmol), 2-chloro-4-methylpyridine(2.6 g, 20 mmol), dicyclohexyl(2′,6′-dimethoxybiphenyl-2-yl)phosphine(S-Phos) (0.36 g, 0.8 mmol), and potassium phosphate (11.4 g, 50 mmol)were mixed in 100 mL of toluene and 10 mL of water. Nitrogen is bubbleddirectly into the mixture for 30 minutes. Next, Pd₂(dba)₃ was added(0.18 g, 0.2 mmol) and the mixture was heated to reflux under nitrogenfor 8 h. The mixture was cooled and the organic layer was separated. Theorganic layers are washed with brine, dried over magnesium sulfate,filtered, and evaporated to a residue. The residue was purified bycolumn chromatography eluting with dichloromethane. 4.7 g of desiredproduct was obtained after purification.

Synthesis of Compound 10

The iridium triflate precursor (2.0 g, 2.7 mmol) and4-methyl-2-(dibenzo[b,d]furan-4-yl)pyridine (2.1 g, 8.1 mmol) were mixedin 60 mL of ethanol. The mixture was heated at reflux for 24 h undernitrogen. Precipitate formed during reflux. The reaction mixture wasfiltered through a celite bed. The product was washed with methanol andhexanes. The solid was dissolved in dichloromethane and purified bycolumn using 1:1 of dichloromethane and hexanes. 1.6 g of pure productwas obtained after the column purification.

Example 5. Synthesis of Compound 29

Synthesis of 4′-bromo-2-nitrobiphenyl

o-iodonitrobenzene (9.42 g, 37.84 mmol), 4-bromobenzeneboronic acid (7.6g, 37.84 mmol), potassium carbonate (21 g, 151.36 mmol) was added to 190mL DME/water (3:2) solution and degassed for 30 minutes. Pd(PPh₃)₄ (437mg, 0.38 mmol) was added to the slurry under nitrogen and the slurry wasdegassed for another 5 minutes. The reaction was refluxed under nitrogenfor 6 h. Content of the flask was filtered through a pad of celite andpartitioned in ethyl acetate and brine. Organic phase was dried overanhydrous Na₂SO₄ and evaporated under vacuum. Crude yellow oil wasflashed over silica gel using 5% ethylacetate/hexane. Final compound wasisolated as colorless oil (9.8 g, 35.4 mmol).

Synthesis of 2-bromo-9H-carbazole

4′-bromo-2-nitrobiphenyl (9.8 g, 35.4 mmol) was refluxed with 30 mLtriethylphosphite overnight. After cooling down the solution to roomtemperature, 40 mL 6(N) HCl was added to it slowly and heated to 80° C.for 3 h. Acidic solution was halfway neutralized with conc. NaOH, restof the acidic solution was neutralized with solid Na₂CO₃. Cloudysolution was extracted three times with ethylacetate (500 mL). Combinedorganic layer was evaporated under vacuum and crude was flashed onsilica gel (15% to 30% ethylacetate/hexane). 4.1 g final compound wasisolated as off white solid.

Synthesis of 2-bromo-9-isobutyl-9H-carbazole

2-bromo-9H-carbazole (4.1 g, 16.74 mmol) was dissolved in DMF. To thestirred solution was slowly added NaH (1.8 g, 75.5 mmol) in 3 portions.Isobutylbromide (4.8 mL, 43.2 mmol) was added to the stirred slurry andafter waiting for 20 minute, warmed up to 60° C. for 4 h. Reactionmixture was cooled to room temperature and carefully quenched with dropwise addition of saturated NH₄Cl solution. Content was then partitionedin brine and ethylacetate. Organic layer was dried over anhydrous Na₂SO₄and evaporated under vacuum. The crude product was flashed over silicagel with 10% ethylacetate/hexane. Final product (4.45 g, 14.8 mmol) wasisolated as white solid.

Synthesis of 9-isobutyl-2-pinacolboron-9H-carbazole

2-bromo-9-isobutyl-9H-carbazole (4.45 g, 14.78 mmol), bisboronpinacolate(4.7 g, 18.5 mmol), potassium acetate (5.8 g, 59.1 mmol) were taken in75 mL anhydrous toluene and degassed for 30 minutes. Pd₂dba₃ (362 mg,0.443 mmol) was added to the slurry under nitrogen and the slurry wasdegassed for another 5 minutes. After overnight reflux, content of thereaction was cooled down and filtered through a celite pad. Toluenesolution was partitioned in water and ethylacetate. Organic layer wasdried over anhydrous Na₂SO₄ and solvent was evaporated under vacuum.Solid crude was flashed in silica gel using 10% ethylacetate/hexane.Isolated solid was subjected to Kugelrohr distillation at 133° C. toremove traces of bisboronpinacolate. Final product (4.77 g, 13.7 mmol)was isolated as off white solid.

Synthesis of 9-isobutyl-2-(pyridine-2-yl)-9H-carbazole

9-isobutyl-2-pinacolboron-9H-carbazole (1.45 g, 4 mmol), 2-bromopyridine(760 mg, 4.8 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (67mg, 0.16 mmol), K₃PO₄.H₂O (3.68 g, 16 mmol) were added to 40 mL mixtureof 9:1 toluene and water. Contents were degassed for 30 minutes beforeaddition of Pd₂dba₃ (37 mg, 0.04 mmol) and degassed for another 5minutes. After overnight reflux, reaction content was cooled to roomtemperature and filtered through a pad of celite. Filtrate waspartitioned in water and ethylacetate. Organic layer was isolated, driedover anhydrous Na₂SO₄ and evaporated under vacuum. Crude was thenflashed over silica gel using 10%-30% ethylacetate/hexane to remove theprotodeborylation product. Final compound (620 mg, 2.1 mmol) wasisolated as white solid.

Synthesis of Compound 29

Carbazole ligand (620 mg, 2.1 mmol) from previous step was dissolved inethanol and Intermediate-1 was added to it under nitrogen. Solution wasthen refluxed overnight. Deep orange color precipitate was filtered outand flashed over silica gel with 50% DCM/hexane. Isolated product wasthen sublimed to give 310 mg 99.7% pure product.

Example 6. Synthesis of Compound 7

Synthesis of Compound 7

The iridium triflate precursor (2.0 g, 2.7 mmol) and4-methyl-2-(dibenzo[b,d]furan-4-yl)pyridine (2.1 g, 8.1 mmol) were mixedin 60 mL of ethanol. The mixture was heated at reflux for 24 h undernitrogen. Precipitate formed during reflux. The reaction mixture wasfiltered through a celite bed. The product was washed with methanol andhexanes. The solid was dissolved in dichloromethane and purified bycolumn using 1:1 of dichloromethane and hexanes. 1.0 g of pure productwas obtained after the column purification.

Example 7. Synthesis of Compound 37

Synthesis of Compound 37

2-(dibenzo[b,d]furan-4-yl)pyridine (5.0 g, 20.39 mmol) and the iridiumtriflate (5.0 g, 5.59 mmol) were placed in a 250 mL round bottom flaskwith 100 mL of a 1:1 solution of ethanol and methanol. The reactionmixture was refluxed for 24 h. A bright yellow precipitate was obtained.The reaction was cooled to room temperature and diluted with ethanol.Celite was added to and the reaction mixture was filtered through asilica gel plug. The plug was washed with ethanol (2×50 mL) followed byhexanes (2×50 mL). The product which remained on the silica gel plug waseluted with dichloromethane into a clean receiving flask. Thedichloromethane was removed under vacuum and the product wasrecrystallized from a combination of dichloromethane and isopropanol.The yellow solid was filtered, washed with methanol followed by hexanesto give bright yellow crystalline product. The product was furtherpurified by recrystallization from toluene followed by recrystallizationfrom acetonotrile to give 1.94 g (37.5% yield) of product with purity99.5% by HPLC.

Device Examples

All example devices were fabricated by high vacuum (<10⁻⁷ Torr) thermalevaporation. The anode electrode is 800 Å of indium tin oxide (ITO). Thecathode consisted of 10 Å of LiF followed by 1000 Å of Al. All devicesare encapsulated with a glass lid sealed with an epoxy resin in anitrogen glove box (<1 ppm of H₂O and O₂) immediately after fabrication,and a moisture getter was incorporated inside the package.

Particular devices are provided wherein an invention compound, Compound1, 2, 4, 7, 10 or 29, is the emitting dopant and H1 is the host. Theorganic stack of Device Examples 1-11 consisted of, sequentially fromthe ITO surface, 100 Å of E1 as the hole injecting layer (HIL), 300 Å of4,4′-bis-[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD) as the holetransport layer (HTL), 300 Å of H1 doped with 7% or 10% of the inventioncompound, an Ir phosphorescent compound, as the emissive layer (EML), 50Å of H1 as the blocking layer (BL) and 400 Å of Alq₃(tris-8-hydroxyquinoline aluminum) as the ETL1.

Comparative Examples 1 and 2 were fabricated similarly to the DeviceExamples, except that E1 and E2. respectively, were used as the emittingdopant.

As used herein, the following compounds have the following structures:

The device structures and device data are summarized below in Table 3and Table 4. Table 3 shows the device structure, and Table 4 shows thecorresponding measured results for the devices. Ex. is an abbreviationof Example.

TABLE 3 Example HIL HTL Host A % BL ETL Example 1 E1 100 Å NPD 300 Å H1Compound 1 H1 50 Å Alq 400 Å 7% Example 2 E1 100 Å NPD 300 Å H1 Compound1 H1 50 Å Alq 400 Å 10% Example 3 E1 100 Å NPD 300 Å H1 Compound 2 H1 50Å Alq 400 Å 7% Example 4 E1 100 Å NPD 300 Å H1 Compound 2 H1 50 Å Alq400 Å 10% Example 5 E1 100 Å NPD 300 Å H1 Compound 4 H1 50 Å Alq 400 Å7% Example 6 E1 100 Å NPD 300 Å H1 Compound 4 H1 50 Å Alq 400 Å 10%Example 7 E1 100 Å NPD 300 Å H1 Compound 7 H1 50 Å Alq 400 Å 7% Example8 E1 100 Å NPD 300 Å H1 Compound 7 H1 50 Å Alq 400 Å 10% Example 9 E1100 Å NPD 300 Å H1 Compound 10 H1 50 Å Alq 400 Å 7% Example 10 E1 100 ÅNPD 300 Å H1 Compound 10 H1 50 Å Alq 400 Å 10% Example 11 E1 100 Å NPD300 Å H1 Compound 29 H1 50 Å Alq 400 Å 10% Comparative E1 100 Å NPD 300Å H1 Compound E1 H1 50 Å Alq 400 Å Example 1 7% Comparative E1 100 Å NPD300 Å H1 Compound E2 H1 50 Å Alq 400 Å Example 2 7%

TABLE 4 At 1000 nits At 40 mA/cm² λ max, CIE V LE EQE PE Lo, Example nmX Y (V) (cd/A) (%) (lm/W) nits RT_(80%), h Ex. 1 532 0.354 0.616 6.160.1 15.9 31 17,382 180 Ex. 2 530 0.367 0.607 6.5 43.2 11.5 21 13,559170 Ex. 3 527 0.355 0.612 6.2 51.7 13.9 26.1 14,565 210 Ex. 4 528 0.3610.609 6 44.4 11.9 23.3 13,618 360 Ex. 5 528 0.348 0.620 5.7 68.7 18.137.7 19,338 98 Ex. 6 528 0.356 0.616 5.2 70.1 18.5 42.4 21,199 96 Ex. 7522 0.326 0.630 5.6 68.2 18.4 38.6 18,431 120 Ex. 8 524 0.336 0.623 5.258.2 15.7 35.0 17,606 200 Ex. 9 522 0.320 0.634 5.4 70.7 19 41.4 19,99675 Ex. 10 522 0.327 0.631 5 71.1 19.1 44.9 21,703 58 Ex. 11 576 0.5380.459 5.6 50.6 19 28.1 14,228 800 Comparative 527 0.344 0.614 6.4 56.715.6 27.6 15,436 155 Ex. 1 Comparative 519 0.321 0.621 6 45.1 12.6 23.613,835 196 Ex. 2

From Device Examples 1-11, it can be seen that the invention compoundsas emitting dopants in green phosphorescent devices provide high deviceefficiency and longer lifetime. In particular, the lifetime, RT_(80%)(defined as the time for the initial luminance, L₀, to decay to 80% ofits value, at a constant current density of 40 mA/cm² at roomtemperature) of devices containing Compounds 1, 2, 7 and 29 are notablyhigher than that measured for Comparative Example 2 which used theindustry standard emitting dopant Ir(ppy)₃. Additionally, Compound 1 inDevice Example 1 achieved high device efficiency (i.e., LE of 60 cd/A at1000 cd/m²), indicating that the inventive compounds comprising a singlesubstituted pyridyl ligand (e.g., pyridyl dibenzofuran) have a highenough triplet energy for efficient green electrophosphorescence.

Additional device structures and device data are summarized below. Thedevice structures and device data are summarized below in Table 5 andTable 6. Table 5 shows the device structure, and Table 6 shows thecorresponding measured results for the devices. Ex. is an abbreviationof Example.

As used herein, the following compounds have the following structures:

H2 is a compound available as NS60 from Nippon Steel Company (NSCC) ofTokyo, Japan.

TABLE 5 Example HIL HTL Host A % BL ETL Example 12 E1 100 Å NPD 300 Å H2Compound 1 H2 100 Å Alq 400 Å 10% Example 13 E1 100 Å NPD 300 Å H2Compound 2 H2 100 Å Alq 400 Å 7% Example 14 E1 100 Å NPD 300 Å H2Compound 2 H2 100 Å Alq 400 Å 10% Example 15 E1 100 Å NPD 300 Å H2Compound 4 H2 100 Å Alq 400 Å 10% Example 16 E1 100 Å NPD 300 Å H2Compound 7 H2 100 Å Alq 400 Å 10% Example 17 E1 100 Å NPD 300 Å H2Compound 10 H2 100 Å Alq 400 Å 10% Example 18 E1 100 Å NPD 300 Å H2Compound 29 H2 100 Å Alq 400 Å 10% Example 19 E3 100 Å NPD 300 Å H1Compound 37 H1 100 Å Alq 400 Å 7% Example 20 E3 100 Å NPD 300 Å H1Compound 37 H1 100 Å Alq 400 Å 10% Example 21 E3 100 Å NPD 300 Å H2Compound 37 H2 100 Å Alq 400 Å 10%

TABLE 6 At 1000 nits At 40 mA/cm² CIE V LE EQE PE Lo, Example λ max, nmX Y (V) (cd/A) (%) (lm/W) nits RT_(80%), h Ex. 12 530 0.361 0.612 4.178.6 20.9 60.0 24,069 220 Ex. 13 526 0.354 0.615 4.7 48.9 13.1 33.014,002 210 Ex. 14 527 0.349 0.620 4.9 49.8 13.3 31.6 14,510 190 Ex. 15528 0.363 0.612 5.1 67.8 18 42.1 21,146 116 Ex. 16 522 0.334 0.626 4.865.9 17.8 43.1 20,136 170 Ex. 17 522 0.333 0.627 5.7 62.1 16.7 34.018,581 98 Ex. 18 576 0.542 0.455 6.4 36.2 13.9 17.9 10,835 740 Ex. 19532 0.386 0.593 5.6 67.8 18.5 37.9 21,426 98 Ex. 20 532 0.386 0.593 5.767.7 18.5 37.5 21,050 103 Ex. 21 532 0.380 0.598 6.5 54.8 14.8 26.716,798 315

From Device Examples 12-21, it can be seen that the invention compoundsas emitting dopants in green phosphorescent devices provide devices withhigh efficiency and long lifetimes. In particular, the lifetime,RT_(80%) (defined as the time for the initial luminance, L₀, to decay to80% of its value, at a constant current density of 40 mA/cm² at roomtemperature) of devices containing Compounds 29 and 37 are notablyhigher than those measured for the Comparative Examples. In particular,Compound 29 in Device Example 18 and Compound 37 in Device Example 21measured 740 h and 315 h, respectively. Devices with Compound 1 in H2,as shown in Example 12, had exceptionally high efficiency, 78.6 cd/A andlong lifetime. It is unexpected that Compound 1 worked extremely well inH2. Additionally, Compounds 1, 4, 7, 29, and 37 in Device Examples 12,15, 17, 19, and 20, respectively, achieved high device efficiency (i.e.,LE of greater than 60 cd/A at 1000 cd/m²), indicating that the inventivecompounds comprising a single substituted pyridyl ligand (e.g., pyridyldibenzofuran) have a high enough triplet energy for efficient greenelectrophosphorescence.

The above data suggests that the heteroleptic iridium complexes providedherein can be excellent emitting dopants for phosphorescent OLEDs,providing devices having improved efficiency and longer lifetime thatmay also have improved manufacturing.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore includes variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

The invention claimed is:
 1. A heteroleptic compound having the formula:

wherein X is NR; wherein R is isobutyl; wherein R₁, R₂, R₃, and R₄ mayrepresent mono, di, tri, or tetra substitutions; and wherein each of R₁,R₂, R₃, and R₄ is independently selected from the group consisting ofhydrogen, alkyl, and aryl.
 2. The heteroleptic compound of claim 1,wherein R₁ and R₄ are independently selected from the group consistingof hydrogen and alkyl having four or fewer carbon atoms.
 3. Theheteroleptic compound of claim 1, wherein R₂ and R₃ are independentlyselected from the group consisting of hydrogen, alkyl having four orfewer carbon atoms and aryl comprising an aryl ring with 5 or 6 atoms inthe aryl ring.
 4. The heteroleptic compound of claim 1, wherein R₁, R₂,R₃, and R₄ are independently selected from the group consisting ofhydrogen, alkyl having four or fewer carbon atoms and aryl comprising anaryl ring with 5 or 6 atoms in the aryl ring.
 5. The heterolepticcompound of claim 1, wherein the compound has the formula:


6. The heteroleptic compound of claim 1, wherein the compound has theformula:


7. The heteroleptic compound of claim 1, wherein the compound has theformula:


8. The heteroleptic compound of claim 1, wherein the compound is


9. The heteroleptic compound of claim 1, wherein the compound isselected from the group consisting of:


10. A first device comprising an organic light emitting device,comprising: an anode; a cathode; and an organic layer, disposed betweenthe anode and the cathode, the organic layer comprising a heterolepticcompound having the formula:

wherein X is NR; wherein R is isobutyl; wherein R₁, R₂, R₃ and R₄ mayrepresent mono, di, tri, or tetra substitutions; wherein each of R₁, R₂,R₃ and R₄ is independently selected from the group consisting ofhydrogen, alkyl, and aryl.
 11. The device of claim 10, wherein theorganic layer is an emissive layer and the heteroleptic compound is anemitting dopant.
 12. The device of claim 10, wherein the organic layerfurther comprises a host.
 13. The device of claim 12, wherein the hostcomprises a triphenylene moiety and a dibenzothiophene moiety.
 14. Thedevice of claim 12, wherein the host has the formula:

wherein R′₁, R′₂, R′₄, and R′₆ may represent mono, di, tri, or tetrasubstitutions; wherein R′₃ and R′₅ may represent mono, di, or trisubstitutions; and wherein each of R′₁, R′₂, R′₃, R′₄, R′₅, and R′₆ isindependently selected from the group consisting of hydrogen, alkyl, andaryl.
 15. A heteroleptic compound having the formula:

wherein X is selected from the group consisting of BR and Se; wherein Ris selected from hydrogen and alkyl; wherein R₁, R₂, R₃, and R₄ mayrepresent mono, di, tri, or tetra substitutions; and wherein each of R₁,R₂, R₃, and R₄ is independently selected from the group consisting ofhydrogen, alkyl, and aryl.
 16. The heteroleptic compound of claim 15,wherein X is Se.
 17. The heteroleptic compound of claim 15, wherein X isBR.
 18. The heteroleptic compound of claim 1 wherein the compound isselected from the group consisting of:


19. The heteroleptic compound of claim 1, wherein the compound isselected from the group consisting of: